Typical Winchester disk drive systems record information on circular information storage disks, each disk having a multiplicity of tracks concentrically located thereon. Each disk drive normally contains a plurality of disks, each disk recording surface having a magnetic head which transfers information to or from an external system. Each magnetic head is located on an arm, and all arms are aligned vertically and attached to a common head positioner assembly. The head positioner assembly is driven by a motor so that the arms and magnetic heads move uniformly across the surfaces of the vertically aligned disks. Head positioner assemblies are usually mounted to rotate the arms and magnetic heads along a circular path over the disks, but some positioner assemblies are driven linearly, producing motion back and forth across the disk.
When the power to the system is turned off, the head positioner assembly is driven by the motor to a landing zone under controlled velocity beyond the innermost or outermost track on which the heads may rest without damaging stored information. The motor drives the head positioner assembly toward the landing zone when power is interrupted, and generally a crash stop is provided to stop movement of the head positioner assembly once it reaches the landing zone. Positioning of the heads on the disks must be very precise, and optimal use of the disks necessitates the smallest possible landing zone to be allocated on each disk. Hence stopping of the head positioner assembly must be accomplished with minimal error.
Typical head positioner stop assemblies must provide two distinct levels of resistance, one for normal power down position limiting (low energy) and another for under loss servo control (electronic failure, high energy). Normal power down position limiting requires absorption of lower angular forces from the head positioner than crash (loss servo control) position limiting.
Previous position limiting methods have provided single level, uniform resistance for both normal and power down position limiting via a spring mechanism or a single stage position limiting arrangement. These methods have proven inadequate in stopping the head positioner under all conditions. Previous single stage stopping methods either provide inadequate resistance under crash conditions which may cause head or disk damage due to excess head deflection or, excess resistance during normal power down may also result in head damage due to high level shock fatigue and incorrect positioning of the heads when the head positioner attains its position limits. Single resistance position limiting arrangements of this type are presented in Chang, U.S. Pat. No. 4,796,131, and Strickler et. al, U.S. Pat. No. 5,134,608.
Spring type position limiting systems or variable damping methods for limiting head position generally provide the aforementioned single level of resistance and take up considerable space in disk drive systems. Spring type position limiting systems exhibiting these characteristics are typified by Ghose et. al, U.S. Pat. No. 4,979,063. As space in a Winchester drive is limited, such a stop arrangement should occupy as little volume as possible.
Accordingly, a principal object of the present invention is to provide a compact method for stopping the angular motion of the head positioner of a hard disk drive during normal power down and crash conditions without excess shock applied to the head positioner, and accomplishing this task using minimal volume within the disk drive.